Engines may be operated using a turbocharger or supercharger to increase mass airflow into the combustion chamber. Turbochargers and superchargers compress intake air entering the engine using an intake compressor. Because this compression may cause an increase in air temperature, a charge air cooler is utilized downstream of the compressor outlet to reduce air temperature before combustion. However, the intake components upstream of the charge air cooler may still be subjected to the high temperature air. In particular, during conditions when engine load is high, and the engine is operating with boost, the boosted intake air can become hot enough to potentially degrade the intake conduit between the compressor outlet and the charge air cooler. Extreme compressor outlet temperatures can also result in compressor coking wherein the oxidation of oil droplets form abrasive deposits on compressor bearings, resulting in premature hardware degradation, and related warranty issues. Accordingly various approaches have been developed for controlling the compressor outlet temperature in a boosted engine system.
One example approach for compressor temperature control is shown by Clement et al. in U.S. Pat. No. 6,076,500. Therein, engine torque is limited based on a measured engine temperature and/or measured intake air temperature. In particular, the permissible engine torque is decreased if the measured intake air temperature exceeds a threshold value.
However, the inventors herein have recognized potential issues with such systems. As one example, it may be difficult to limit engine torque while balancing the conflicting needs to maintain engine performance and maintain engine component integrity. For example, during conditions when engine load is high, engine torque may be decreased to lower levels responsive to an elevated intake air temperature so as to protect the engine against overheating that can occur if the engine load remains high for an extended period of time. However, if the high load condition is transient, the actual heating incurred at the compressor outlet may be significantly lower than the heating expected based on the air temperature measurement.
Specifically, current measurements of the intake air temperature may not reflect the actual temperature of components in the intake due to the thermodynamics of the intake system (e.g., delay in heating or cooling of intake components relative to heating or cooling of intake air). Thus, the rate at which the intake air changes temperature may be higher than that of the intake components. For example, as a driver requested torque increases, and an amount of boost increases to meet the torque demands, the intake air temperature may increase more rapidly than the engine intake components, such as the compressor and the intake conduit tubing included between the compressor and the charge air cooler. As such, the intake components may be at a lower temperature than the intake air during the increase in torque demand, and may not reach thermal equilibrium with the intake air until after the intake air temperature has remained relatively constant for a duration. Thus, the intake components may not reach potentially degrading temperatures until after the engine has been operating at high load for a threshold duration. As a result, when a high engine load is requested for only a short duration, engine torque may be overly limited, degrading the boosted engine performance.
In one example, the issue described above may be at least partly addressed by a method for an engine comprising: adjusting an engine torque output based on a future compressor outlet temperature profile to maintain an actual compressor outlet temperature below a threshold, the future compressor outlet temperature profile based on current and predicted engine operating conditions estimated based on inputs from external vehicle. In this way, compressor outlet temperature may be more precisely regulated without unnecessarily restricting engine torque output.
As one example, during boosted engine operation, an engine controller may model a compressor outlet temperature (or temperature profile) based on current and predicted engine operating conditions including current and future torque requirements. Future torque requirements may be estimated based on vehicle-specific information such as driver behavior history, engine knocking history, etc., as well as information provided by external vehicle communication, such as navigation route, road-grade information, traffic information, etc. The information provided via external vehicle communication may be retrieved using a navigation system communicatively coupled to the controller, wireless communication, vehicle-to-vehicle communication, etc. The future torque requirement estimates are used in conjunction with current vehicle measurements to model the compressor outlet temperature over a future horizon (which includes an upcoming segment of vehicle travel). In particular, the engine torque is used to determine an engine mass-flow rate, which in turn is used with a barometric pressure estimate to determine an exhaust back-pressure estimate. The exhaust back-pressure is then used to infer a compressor pressure ratio, and therefrom an instantaneous compressor outlet temperature may be modeled. The modeled compressor outlet temperature may then be filtered to model an intake conduit temperature (including a temperature of the material in the intake conduit coupling the compressor outlet to the charge air cooler, as well as a temperature of the gases flowing in the conduit) over the future horizon. The controller may then limit an engine torque output based on the modeled compressor outlet temperature profile so as to maintain each of the compressor outlet temperature and the intake conduit temperature below respective thresholds. In another example, the engine torque output may be, additionally or optionally, adjusted to maintain a throttle inlet pressure. For example, the controller may limit the engine torque via adjustments to an intake throttle and/or an exhaust wastegate actuator.
In this way, engine torque output can be more accurately adjusted based on the future compressor outlet temperature profile. A technical effect of increasing torque output while maintaining the temperature of intake components below respective threshold temperatures is achieved by predicting temperatures of one or more intake components based on predicted engine operating conditions. In addition, the engine torque limiting can be more precisely controlled to be aggressive enough to deliver the demanded torque while reducing intake conduit degradation. In this way, overheating of engine components is reduced and engine torque output is not excessively limited.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.